An epoxy resin has been widely employed as adhesives, coatings, casting materials, molding compound for encapsulation, resin for embedding, and laminating materials because of an excellent adhesive property with metallic materials and glass, high mechanical strength, and excellent workability in curing, etc.
An epoxy resin is designed as being cured by mixing with an amine-curing agent, a mercaptan-curing agent, a phenol resin-curing agent, and an acid anhydride-curing agent in response to the uses of the epoxy resin, and those are occasionally employed together with a tertiary amine-, quaternary ammonium-, tertiary phosphine-, imidazole-, and azabicyclo compound-curing accelerator as a catalyst for the purpose of the addition of curability at low temperature and curability in a short time of period, etc.
In recent years, requirements for an improvement in characteristics have become more advanced in a variety of utilization fields for a cured article prepared from an epoxy resin. In the system in which an amine-curing agent is contained, there also increase fields in which characteristics cannot be satisfied by conventional products because of a problem such as storage stability for a long term caused by a great change of viscosity after the amine-curing agents are contained. Further, in a system which employs an acid anhydride- or phenol resin-curing agent, etc, there is a similar problem in curing accelerators mainly employed until now, which include tertiary amine-, quaternary ammonium-, tertiary phosphine-, quaternary phosphonium-, imidazole-, and azabicyclo compound-ones. For solving the problem, it has been proposed a modified epoxy adduct, a modified aliphatic amine, a modified polyamide amine, a mannich-modified amine, a thiourea-modified amine, a Schiff-modified amine (obtained by ketiminization), a Michael addition-modified amine, and a quaternary salt of imidazoles, etc.
There is an attempt that an N-substituted melamine is employed as an amine-curing agent for improving a storage stability after mixing and workability, etc. As such epoxy resin compositions, Japanese Patent Application Laid-open No. Sho 56-72019 discloses an epoxy resin composition in which an N-substituted melamine is contained. British Patent No. 1192790 discloses an epoxy resin composition in which an N-substituted melamine having at least two primary amino groups or guanamine, etc. is contained as an amine-curing agent.
There is an attempt that an N-substituted melamine is employed as a curing accelerator in an epoxy compound/phenol resin curing system for improving a stability such as a pot life after mixing and workability. As such epoxy resin compositions, Japanese Patent Application Laid-open No. Sho 60-202117 discloses an epoxy resin composition in which an N-substituted melamine and a novolak-type phenol resin are contained.
In the case of preparing an epoxy compound/acid anhydride-cured resin, if a tertiary amine-, a quaternary ammonium-, a quaternary phosphonium-, imidazole-, and azabicyclo compound-curing accelerators, etc. are not contained, reactivity of an epoxide with an acid anhydride is poor, productivity exceedingly lowers in a cured resin, and it becomes substantially difficult to prepare the cured resin. However, if such the curing accelerator is employed together as a catalyst, reaction usually proceeds even at a relatively low temperature, viscosity increases with a lapse of time and, further, gelling is caused, resulting in that a composition becomes incapable of employing.
Further, as a method for prolonging a pot life, although there is a means in which a very small amount of the above-mentioned curing accelerator or a curing accelerator having a low activity is employed, it is apt to cause defects such as bubbles and cracks, etc, particularly, in a curing reaction at high temperatures.
In the above-mentioned British Patent No. 1192790, it is disclosed an epoxy compound/acid anhydride-curing resin system and an epoxy compound/amine-curing resin system, and it is disclosed an epoxy resin composition in which an N-substituted melamine having at least two primary amino groups or guanamine, etc. is mixed as an amine-curing agent together with a benzoyl urea- and a sulfonyl urea-curing accelerator. In the curing resin systems, it is exemplified that the N-substituted melamine having at least two primary amino groups or guanamine, etc. shows an excellent property, and in Examples for the acid anhydride-curing system, it is disclosed a combination with the benzoyl urea- or sulfonyl urea-curing accelerator.
The present invention uses an acid anhydride-curing agent in an epoxy compound and contain a substituted triazine compound having a specified structure in a limited amount as a curing accelerator, whereby aiming to provide an epoxy/acid anhydride composition which is excellent in a pot life after the curing agent is contained, storage stability, and workability, and an epoxy/acid anhydride resin composition prepared by thermosetting the epoxy/acid anhydride composition, and in which defects such as bubbles and cracks are not caused in a cured resin at all.